Seed layer-based alpha-phase tantalum superconducting thin film, preparation method and application thereof

Abstract

The invention provides an alpha-phase tantalum superconducting thin film based on a seed layer, a preparation method and application thereof. The preparation method comprises the following steps: S1, providing a substrate; s2, growing a niobium metal seed layer on the upper surface of the substrate by adopting a direct current magnetron sputtering method; and S3, growing an alpha-phase tantalum superconducting film on one surface, far away from the substrate, of the niobium metal seed layer by adopting a direct-current magnetron sputtering method. The niobium metal seed layer and the alpha-phase tantalum superconducting thin film are sequentially grown on the substrate by adopting a direct-current magnetron sputtering process, and interlayer lattice mismatch of the alpha-phase tantalum superconducting thin film can be reduced by introducing the niobium metal seed layer, so that the alpha-phase tantalum superconducting thin film with single (110) crystal phase growth is prepared at room temperature; in addition, direct-current magnetron sputtering equipment with multiple sputtering coating chambers can be used, sputtering is sequentially carried out at the room temperature by adopting a direct-current magnetron sputtering process, the equipment cost is greatly reduced, the process stability is high, and a more reliable material basis is provided for development of superconducting quantum calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetron sputtering coating, and in particular relates to an alpha-phase tantalum superconducting film based on a seed layer, a preparation method and an application thereof. Background Art

[0002] In the field of superconducting quantum computing, the loss of the device has a crucial impact on the computing performance. In order to realize quantum bit devices with long coherence time, low-loss superconducting metal materials are usually used to prepare the required resonant cavity and capacitor. At present, common superconducting metal materials include niobium (Nb), aluminum (Al), tantalum (Ta), titanium nitride (TiN), niobium titanium nitride (NbTiN), etc. Among them, the α-phase tantalum superconducting film with a single crystal orientation has a low surface resistance, which enables it to reduce energy loss in superconducting quantum computing, thereby extending the coherence time of the quantum bit, and therefore is highly favored.

[0003] Epitaxial coating technology is a technology used to grow thin films with specific crystal structures and orientations on substrates. It is an effective method for obtaining metal films with a single crystal orientation. Common epitaxial coating methods include molecular beam epitaxy, laser pulse deposition, magnetron sputtering, etc.; molecular beam epitaxy is to deposit atoms or molecular beams of evaporated source materials directly onto a heated substrate and grow them in a vacuum, which is suitable for growing ultra-thin films and multilayer structures; laser pulse deposition uses high-energy laser pulses to irradiate the target material to generate plasma, and the atoms or molecules in the plasma are deposited on the substrate to form a thin film; and magnetron sputtering uses the action of magnetic and electric fields to bombard the surface of the target material with inert gas ions, and the sputtered atoms are deposited on the substrate to form a thin film.

[0004] At present, magnetron sputtering is usually used to prepare single-crystalline tantalum superconducting films. However, this technology can only obtain β-phase tantalum films at room temperature, and the substrate must be heated to above 400°C to prepare α-phase tantalum superconducting films. This process not only has high requirements on equipment, but also has poor process stability, which limits its promotion in practical applications.

[0005] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0007] In view of the shortcomings of the prior art mentioned above, the purpose of the present invention is to provide an α-phase tantalum superconducting film based on a seed layer, a preparation method and its application, so as to solve the problems that the existing preparation process of α-phase tantalum superconducting film requires a high temperature, has high requirements on equipment and poor process stability.

[0008] To achieve the above-mentioned object and other related objects, the present invention provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer, the preparation method comprising the following steps:

[0009] S1. providing a substrate;

[0010] S2, growing a niobium metal seed layer on the upper surface of the substrate by using a DC magnetron sputtering method;

[0011] S3. Using a DC magnetron sputtering method, grow an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate.

[0012] Preferably, the substrate in step S1 includes one of a sapphire substrate, a silicon substrate, a thermally oxidized silicon substrate, and a magnesium oxide substrate.

[0013] Preferably, the equipment used for the DC magnetron sputtering method in step S2 is a DC magnetron sputtering equipment, the DC magnetron sputtering equipment comprises a niobium sputtering coating chamber, and the target material used in the niobium sputtering coating chamber is a niobium metal target material;

[0014] The specific steps of growing a niobium metal seed layer on the upper surface of the substrate include:

[0015] S21, placing the substrate in the niobium sputtering coating chamber, and pumping the vacuum degree to 3×10 -5 Below Pa;

[0016] S22, introducing working gas into the niobium sputtering coating chamber to maintain the pressure in the niobium sputtering coating chamber at a preset value;

[0017] S23, applying current to the target material, performing sputtering coating at a certain sputtering power, so that niobium metal is sputtered from the target material to the upper surface of the substrate.

[0018] Preferably, the pressure in step S22 is maintained at 0.3Pa-1Pa; the current applied in step S23 is 0.5A-2.5A, the sputtering power is 300W-1000W, and the sputtering coating rate is 0.5nm / s-2nm / s.

[0019] Preferably, the thickness of the niobium metal seed layer in step S2 is 5 nm to 50 nm.

[0020] Preferably, the device used for the DC magnetron sputtering method in step S3 is a DC magnetron sputtering device, the DC magnetron sputtering device comprises a tantalum sputtering coating chamber, and the target material used in the tantalum sputtering coating chamber is a tantalum metal target material;

[0021] The specific steps of growing an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate include:

[0022] S31, transferring the sample with the niobium metal seed layer grown thereon to the tantalum sputtering coating chamber, and pumping the vacuum degree thereof to 3×10 -5 Below Pa;

[0023] S32, introducing working gas into the tantalum sputtering coating chamber to maintain the pressure in the tantalum sputtering coating chamber at a preset value;

[0024] S33, applying current to the target material, and performing sputtering coating at a certain sputtering power, so that the tantalum metal is sputtered from the target material to the side of the niobium metal seed layer away from the substrate.

[0025] Preferably, the pressure in step S32 is maintained at 0.3Pa to 1Pa; the current applied in step S33 is 0.5A to 2.5A, the sputtering power is 300W to 1000W, and the sputtering coating rate is 0.5nm / s to 2nm / s.

[0026] Preferably, the thickness of the α-phase tantalum superconducting thin film in step S3 is 100 nm to 300 nm.

[0027] The present invention also provides an α-phase tantalum superconducting film prepared by adopting the above-mentioned method for preparing an α-phase tantalum superconducting film based on a seed layer.

[0028] In addition, the present invention also provides an application of an α-phase tantalum superconducting film, and the application of the α-phase tantalum superconducting film in a superconducting quantum device, wherein the α-phase tantalum superconducting film is prepared by adopting the above-mentioned method for preparing an α-phase tantalum superconducting film based on a seed layer.

[0029] As described above, the α-phase tantalum superconducting film based on the seed layer, the preparation method and the application thereof of the present invention have the following beneficial effects:

[0030] The present invention adopts a direct current magnetron sputtering process to sequentially grow a niobium metal seed layer and an α-phase tantalum superconducting film on a substrate. By introducing the niobium metal seed layer, the interlayer lattice mismatch of the α-phase tantalum superconducting film can be reduced, and the α-phase tantalum superconducting film grown in a single (110) crystal phase can be prepared at room temperature. The XRD spectrum of the prepared (110) crystal phase α-phase tantalum superconducting film has a characteristic diffraction peak at 38.47°, and the error is ±0.25°. In addition, the present invention can also use a direct current magnetron sputtering device with multiple sputtering coating chambers, and adopt a direct current magnetron sputtering process to perform sputtering sequentially at room temperature, which greatly reduces the equipment cost and has high process stability, thereby providing a more reliable material basis for the development of superconducting quantum computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Shown is a process flow chart of preparing an α-phase tantalum superconducting thin film based on a seed layer according to the present invention.

[0032] Figure 2 Shown is the XRD pattern of the α-phase tantalum superconducting thin film prepared in Example 1 of the present invention.

[0033] Figure 3 An atomic force microscope image of the α-phase tantalum superconducting thin film prepared in Example 1 of the present invention is shown.

[0034] Figure 4 Shown is the XRD pattern of the α-phase tantalum superconducting thin film prepared in Example 2 of the present invention.

[0035] Figure 5 An atomic force microscope image of the α-phase tantalum superconducting thin film prepared in Example 2 of the present invention is shown.

[0036] Figure 6 It shows the changing trend of the internal quality factor of the superconducting coplanar waveguide resonant cavity at different frequencies in Application Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods in the following examples without specifying specific conditions are generally carried out under conventional conditions or under conditions recommended by the manufacturers.

[0039] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0040] See also Figure 1 The present invention provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer, the preparation method comprising the following steps:

[0041] S1. providing a substrate;

[0042] S2, growing a niobium metal seed layer on the upper surface of the substrate by using a DC magnetron sputtering method;

[0043] S3. Using a DC magnetron sputtering method, grow an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate.

[0044] Specifically, a niobium metal seed layer is introduced on the upper surface of the substrate, and the seed layer forms a niobium metal layer with a lattice constant of 0.331 nm on the surface of the substrate. The structure is consistent with the lattice constant of tantalum metal of 0.331 nm. The lattice matching effect of the niobium metal layer and the tantalum metal is used to promote the growth of the α-phase tantalum superconducting film on the niobium metal seed layer along the lattice stacking direction of the seed layer to form an α-phase tantalum superconducting film with a single crystal orientation, thereby realizing the preparation of a single crystal phase grown α-phase tantalum superconducting film at room temperature.

[0045] As an example, the substrate in step S1 includes one of a sapphire (Al2O3) substrate, a silicon (Si) substrate, a thermally oxidized silicon (Si / SiO2) substrate, and a magnesium oxide (MgO) substrate.

[0046] Specifically, the sapphire substrate is a single crystal form of aluminum oxide, ie, an Al2O3 substrate.

[0047] As an example, the substrate in step S1 needs to be cleaned chemically and / or plasma cleaned to remove stains on the surface of the substrate; wherein the chemical cleaning includes cleaning with a concentrated sulfuric acid-hydrogen peroxide mixed solution or a hydrofluoric acid cleaning solution; and the plasma cleaning includes cleaning with a radio frequency glow plasma or an ion beam cleaning solution.

[0048] Specifically, the concentrated sulfuric acid-hydrogen peroxide mixed solution is usually called the piranha solution, which is usually prepared by slowly adding 30% hydrogen peroxide solution to 98% concentrated sulfuric acid in a volume ratio. The volume ratio of concentrated sulfuric acid to hydrogen peroxide solution is usually 9:1, 7:3, or 3:1. The hydrofluoric acid cleaning solution is mainly composed of hydrofluoric acid, and can also be a buffered solution mixed with ammonium fluoride (NH4F) and hydrofluoric acid (HF). The buffered HF etching solution is composed of 6 volumes of 40% ammonium fluoride solution and 1 volume of 49% hydrofluoric acid solution. As an example, the equipment used for the DC magnetron sputtering method in step S2 is a DC magnetron sputtering equipment, and the DC magnetron sputtering equipment includes a niobium sputtering coating chamber, and the target material used in the niobium sputtering coating chamber is a niobium metal target;

[0049] The specific steps of growing a niobium metal seed layer on the upper surface of the substrate include:

[0050] S21, placing the substrate in the niobium sputtering coating chamber, and pumping the vacuum degree to 3×10 -5 Below Pa;

[0051] S22, introducing working gas into the niobium sputtering coating chamber to maintain the pressure in the niobium sputtering coating chamber at a preset value;

[0052] S23, applying current to the target material, performing sputtering coating at a certain sputtering power, so that niobium metal is sputtered from the target material to the upper surface of the substrate.

[0053] Specifically, the sputtering coating chamber of the DC magnetron sputtering device may include one or multiple chambers, that is, a multi-chamber DC magnetron sputtering device is used, and samples are transferred between chambers through a transfer arm.

[0054] In a specific embodiment of the present invention, before step S21, the substrate is placed in the sample injection chamber and evacuated to 1e - 4 Pa or less, then step S21 is performed to transfer the substrate to a niobium sputtering coating chamber.

[0055] Before step S22, the distance between the substrate and the target material needs to be adjusted, and then step S22 is performed.

[0056] Before performing step S23, the method also includes using a baffle to shield the niobium target and the substrate, passing a specific power through the target for pre-sputtering to clean the target surface, then removing the baffle between the target and the substrate to make the substrate face the target surface, and then performing step S23.

[0057] The DC magnetron sputtering equipment also has a cooling function, including water cooling of the substrate back plate and helium blowing cooling of the sample surface; after step S23, the power input to the target material is turned off, the process gas is stopped, the sputtering of the entire niobium metal seed layer is completed, and then cooling is performed.

[0058] As an example, the pressure value in step S22 is maintained at 0.3Pa to 1Pa; the current applied in step S23 is 0.5A to 2.5A, the sputtering power is 300W to 1000W, and the sputtering coating rate is 0.5nm / s to 2nm / s.

[0059] Specifically, the pressure value maintained in the niobium sputtering coating chamber in step S22 may include values ​​within any range such as 0.3Pa, 0.5Pa, 0.7Pa, 0.9Pa, 1Pa, etc.; the current applied to the target material in step S23 may include values ​​within any range such as 0.5A, 1A, 1.5A, 2A, 2.5A, etc., and the sputtering power may include values ​​within any range such as 300W, 400W, 500W, 600W, 800W, 900W, 1000W, etc.; the sputtering coating rate may include values ​​within any range such as 0.5nm / s, 0.6nm / s, 0.8nm / s, 1.0nm / s, 1.5nm / s, 1.8nm / s, 2nm / s, etc.

[0060] In addition, in a specific embodiment of the present invention, a DC magnetron sputtering method is used to grow a niobium metal seed layer on the upper surface of the substrate at a growth temperature of room temperature, usually around 25°C. Since the temperature will rise during the actual preparation process, water cooling is generally used to ensure that the temperature fluctuation is within the range of 5°C.

[0061] As an example, the thickness of the niobium metal seed layer in step S2 is 5 nm to 50 nm.

[0062] Specifically, the thickness of the niobium metal seed layer grown on the upper surface of the substrate may be within any range of 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 45 nm, 50 nm, etc.

[0063] Specifically, when the lattice mismatch between the substrate and the α-phase tantalum superconducting film is large, a niobium metal seed layer with a small lattice mismatch with the α-phase tantalum superconducting film is formed on the substrate, thereby assisting the growth of the α-phase tantalum superconducting film; when the thickness of the niobium metal seed layer is thin, the overall film properties (such as resistivity, critical temperature of the superconducting film, etc.) are mainly determined by the α-phase tantalum superconducting film, and when the thickness of the niobium metal seed layer is thick, the overall film properties are jointly determined by the niobium metal seed layer, the α-phase tantalum superconducting film and the interface characteristics. In addition, when the niobium metal seed layer is thin, its surface roughness is small, and the interface between the niobium metal seed layer and the α-phase tantalum superconducting film is better, but because the substrate lattice structure provided by the thinner niobium metal seed layer is not as complete as the thicker niobium metal seed layer, the properties of the α-phase tantalum superconducting film obtained on the thicker niobium metal seed layer are better. Therefore, the thickness of the niobium metal seed layer is affected by many factors.

[0064] As an example, the device used for the DC magnetron sputtering method in step S3 is a DC magnetron sputtering device, the DC magnetron sputtering device includes a tantalum sputtering coating chamber, and the target material used in the tantalum sputtering coating chamber is a tantalum metal target material;

[0065] The specific steps of growing an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate include:

[0066] S31, transferring the sample with the niobium metal seed layer grown thereon to the tantalum sputtering coating chamber, and pumping the vacuum degree thereof to 3×10 -5 Below Pa;

[0067] S32, introducing working gas into the tantalum sputtering coating chamber to maintain the pressure in the tantalum sputtering coating chamber at a preset value;

[0068] S33, applying current to the target material, and performing sputtering coating at a certain sputtering power, so that the tantalum metal is sputtered from the target material to the side of the niobium metal seed layer away from the substrate.

[0069] Specifically, the DC magnetron sputtering equipment used in step S2 and step S3 can be the same equipment, including two sputtering coating chambers, one niobium sputtering coating chamber, and the other tantalum sputtering coating chamber. After the niobium metal seed layer is completed in the niobium sputtering coating chamber, the sample is directly transferred to the tantalum sputtering coating chamber through the transfer arm for sputtering; of course, the target material in the niobium sputtering coating chamber is niobium metal, and the target material in the tantalum sputtering coating chamber is tantalum metal.

[0070] In a specific embodiment of the present invention, before performing step S32, the distance between the sample and the target material needs to be adjusted, and then step S32 is performed; before performing step S33, it also includes using a baffle to shield the tantalum target material and the sample, passing a specific power into the tantalum target material for pre-sputtering to clean the target surface, and then removing the baffle between the tantalum target material and the sample to make the niobium metal seed layer in the sample facing the target surface away from the substrate, and then performing step S33; after step S33, the input power to the tantalum target material is turned off, the process gas is stopped, the sputtering of the tantalum metal layer is completed, and after sufficient cooling, the newly formed sample is heat transferred into the sampling chamber, and then nitrogen is passed to break the vacuum and take out the sample.

[0071] In addition, in a specific embodiment of the present invention, the DC magnetron sputtering method is used to grow the α-phase tantalum superconducting thin film on the side of the niobium metal seed layer away from the substrate at a growth temperature of room temperature, usually 20-30°C.

[0072] As an example, the pressure in step S32 is maintained at 0.3Pa to 1Pa; the current applied in step S33 is 0.5A to 2.5A, the sputtering power is 300W to 1000W, and the sputtering coating rate is 0.5nm / s to 2nm / s.

[0073] Specifically, the pressure in the tantalum sputtering coating chamber maintained in step S32 may include values ​​within any range such as 0.3Pa, 0.5Pa, 0.7Pa, 0.9Pa, 1Pa, etc.; the current for the target material time in step S23 may include values ​​within any range such as 0.5A, 1A, 1.5A, 2A, 2.5A, etc., and the sputtering power may include values ​​within any range such as 300W, 400W, 500W, 600W, 800W, 900W, 1000W, etc.; the sputtering coating rate may include values ​​within any range such as 0.5nm / s, 0.6nm / s, 0.8nm / s, 1.0nm / s, 1.5nm / s, 1.8nm / s, 2nm / s, etc.

[0074] As an example, the thickness of the α-phase tantalum superconducting film in step S3 is 100 nm to 300 nm.

[0075] Specifically, the thickness of the α-phase tantalum superconducting film may include values ​​within any range such as 100nm, 110nm, 150nm, 200nm, 250nm, 280nm, 300nm, etc.; when the thickness of the α-phase tantalum superconducting film is too thin, its superconducting critical temperature is low and the superconductivity is incomplete; the thicker the α-phase tantalum superconducting film, the smaller its resistivity, and the closer the superconducting critical temperature is to the theoretical value of the bulk material, corresponding to better superconductivity; but as the thickness of the α-phase tantalum superconducting film increases, its surface roughness will also increase. In the subsequent device preparation process, excessive surface roughness will bring about undesirable interfaces and surfaces, so the thickness of the α-phase tantalum superconducting film needs to be moderate.

[0076] The present invention also provides an α-phase tantalum superconducting film prepared by the above-mentioned method for preparing an α-phase tantalum superconducting film based on a seed layer. Specifically, the α-phase tantalum superconducting film is grown based on a niobium metal seed layer, the thickness of the niobium metal seed layer is 5nm to 50nm, the thickness of the α-phase tantalum superconducting film is 100nm to 300nm, and the prepared α-phase tantalum superconducting film is a tantalum film with a (110) crystal phase, and its XRD spectrum has a characteristic diffraction peak at 38.47°, with an error of ±0.25°.

[0077] In addition, the present invention also provides an application of an α-phase tantalum superconducting film, and the application of the α-phase tantalum superconducting film in a superconducting quantum device, wherein the α-phase tantalum superconducting film is prepared by adopting the above-mentioned method for preparing an α-phase tantalum superconducting film based on a seed layer.

[0078] Specifically, the application of α-phase tantalum superconducting film in superconducting quantum devices includes applications in coplanar waveguide resonant cavity, superconducting quantum chip, and low-temperature physics technology. The coplanar waveguide resonant cavity is an important microwave device, which is often used in superconducting quantum computing; the superconducting quantum chip is the core of the superconducting quantum device, which integrates key components such as superconducting quantum bits, couplers, and resonant cavities; low-temperature physics technology is the basic condition for the operation of superconducting quantum devices. Superconducting quantum devices usually need to work in an extremely low temperature environment (such as close to absolute zero) to maintain the superconducting properties of superconducting materials and reduce thermal noise.

[0079] In order to better understand the α-phase tantalum superconducting film based on the seed layer, the preparation method and the application thereof in the present invention, the α-phase tantalum superconducting film based on the seed layer, the preparation method and the application thereof in the present invention are described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0080] Example 1

[0081] This embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer, comprising the following steps:

[0082] S1. Provide a silicon substrate, use a piranha solution prepared by mixing 98% concentrated sulfuric acid and 30% hydrogen peroxide solution in a ratio of 3:1, heat it to 70°C, put the silicon substrate into the solution and clean it for 20 minutes. After cleaning, put the silicon substrate into deionized water for ultrasonic treatment for 2 hours to remove the residual solution on the surface of the silicon substrate, and then use a nitrogen gun to blow dry the silicon substrate; put the silicon substrate cleaned with the piranha solution into a buffered HF etching solution for cleaning for 10 minutes. After cleaning, put it into deionized water for ultrasonic treatment for 2 hours to remove the residual solution on the surface of the silicon substrate, and then use a nitrogen gun to blow it dry.

[0083] S2. A niobium metal seed layer is grown on the surface of a silicon substrate by using a DC magnetron sputtering method, specifically comprising the following steps:

[0084] S21, load the silicon substrate onto the loading plate of the sample chamber of the magnetron sputtering equipment, close the sample chamber and evacuate to 1e -4 Pa, and then place the silicon substrate in a niobium sputtering coating chamber and pump the vacuum degree to 3×10 -5 Pa or less, adjusting the distance between the silicon substrate and the niobium target to a predetermined distance of 200 mm;

[0085] S22, introducing working gas into the niobium sputtering coating chamber to maintain the pressure in the niobium sputtering coating chamber at 0.5 Pa;

[0086] S23. Use a baffle to shield the niobium target and the silicon substrate, pass a current of 2A through the niobium target to reach a power of 600W, and perform pre-sputtering for 1 minute to clean the target surface. Then remove the baffle between the niobium target and the silicon substrate to make the silicon substrate face the niobium target surface. Maintain a sputtering power of 600W for sputtering coating to sputter niobium metal from the target to the upper surface of the substrate. After sputtering at a sputtering coating rate of 1nm / s for 5s, turn off the input power to the niobium target, stop the process gas, complete the entire niobium metal seed layer with a thickness of 5nm, and finally fully cool the formed sample for 20min.

[0087] S3, using a DC magnetron sputtering method to grow an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate, specifically comprising the following steps:

[0088] S31, transfer the sample with the niobium metal seed layer to the tantalum sputtering coating chamber, and draw the vacuum degree to 3×10 -5 Pa or less, adjust the distance between the sample and the tantalum target to 200 mm;

[0089] S32, introducing working gas into the tantalum sputtering coating chamber to maintain the pressure in the tantalum sputtering coating chamber at 0.5 Pa;

[0090] S33. Use a baffle to shield the tantalum target and the sample, pass a current of 2A through the tantalum target to reach a power of 500W, and perform pre-sputtering for 1 minute to clean the target surface. Then remove the baffle between the tantalum target and the sample to make the side of the niobium metal seed layer growing away from the substrate face the tantalum target surface. Maintain a sputtering power of 500W for sputtering coating, so that tantalum metal is sputtered from the target to the side of the niobium metal seed layer away from the substrate. After sputtering for 150 seconds at a sputtering coating rate of 1nm / s, turn off the input power to the tantalum target, stop the process gas, and complete a 150nm thick α-phase tantalum superconducting film; then cool it sufficiently and pass it into the injection chamber, then fill it with nitrogen to break the vacuum and take out the sample.

[0091] The crystal structure of the α-phase tantalum superconducting film prepared in this embodiment was analyzed by X-ray diffractometer. Figure 2 The X-ray diffraction peaks from left to right are the α-phase Ta (110) diffraction peak, the silicon substrate Si (400) diffraction peak, and the α-phase Ta (220) diffraction peak. The (220) α-phase tantalum superconducting film diffraction peak in the figure is a secondary diffraction peak.

[0092] The surface morphology of the α-phase tantalum superconducting film prepared in this embodiment was analyzed using an atomic force microscope. Figure 3 The surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.8 nm, and the surface morphology has small fluctuations and good uniformity.

[0093] Example 2

[0094] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment is different from that in Embodiment 1 in that: the substrate in step S1 is a sapphire substrate, and a piranha solution prepared by mixing 98% concentrated sulfuric acid and 30% hydrogen peroxide solution in a ratio of 3:1 is used, heated to 70° C., and the sapphire substrate is placed in the solution for cleaning for 20 minutes. After the cleaning is completed, the sapphire substrate is placed in deionized water for ultrasonic treatment for 2 hours to remove the residual solution on the surface of the sapphire substrate, and then the sapphire substrate is blown dry using a nitrogen gun; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0095] The crystal structure of the α-phase tantalum superconducting film prepared in this embodiment was analyzed by X-ray diffractometer. Figure 4 , the X-ray diffraction peaks from left to right are respectively the α-phase Ta (110) diffraction peak, the sapphire substrate Al2O3 (0006) diffraction peak, the α-phase Ta (220) diffraction peak, and the sapphire substrate Al2O3 (00012) diffraction peak; the α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and the (220) α-phase tantalum superconducting film diffraction peak in the figure is a secondary diffraction peak.

[0096] The surface morphology of the α-phase tantalum superconducting film prepared in this embodiment was analyzed using an atomic force microscope. Figure 5 The surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.5 nm, and the surface morphology has small fluctuations and good uniformity.

[0097] Since the lattice constant of silicon is 0.543nm; the lattice constant of sapphire is 0.476nm, the lattice constant of niobium is 0.331nm, and the lattice constant of tantalum is 0.331nm; generally speaking, the smaller the lattice mismatch between the substrate and the α-phase tantalum superconducting film, the better the epitaxy of the deposited α-phase tantalum superconducting film, because the lattice mismatch is small, the lattice stacking of the film is more ordered, and thus the surface roughness is smaller, that is, compared with Example 1, the root mean square roughness of the surface of the α-phase tantalum superconducting film prepared in this embodiment is smaller than that in Example 1; the lattice mismatch between the silicon substrate and niobium metal and tantalum metal is greater than the lattice mismatch between the sapphire substrate and niobium metal and tantalum metal, so the epitaxy of the deposited α-phase tantalum superconducting film is relatively poor, the film stacking disorder is higher, and the surface roughness is greater.

[0098] Example 3

[0099] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment differs from that in Embodiment 2 in that: in step S33, a current of 1.5 A is passed, and sputtering coating is performed at a sputtering power of 370 W, and finally an α-phase tantalum superconducting thin film with a thickness of 150 nm is obtained; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0100] The α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and has a characteristic diffraction peak at 38.44°; the surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.634 nm, and the surface morphology has small fluctuations and good uniformity.

[0101] Example 4

[0102] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment differs from that in Embodiment 2 in that: in step S33, a current of 2.5 A is passed, and sputtering coating is performed at a sputtering power of 625 W, and finally an α-phase tantalum superconducting thin film with a thickness of 150 nm is obtained; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0103] The α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and has a characteristic diffraction peak at 38.35°; the surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.602nm, and the surface morphology has small fluctuations and good uniformity.

[0104] Example 5

[0105] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment differs from that in Embodiment 2 in that: the pressure in step S32 is maintained at 0.3 Pa; in step S33, a current of 1.5 A is passed, and sputtering coating is performed at a sputtering power of 390 W, and finally an α-phase tantalum superconducting thin film with a thickness of 150 nm is obtained; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0106] The α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and has a characteristic diffraction peak at 38.30°; the surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.655 nm, and the surface morphology has small fluctuations and good uniformity.

[0107] Example 6

[0108] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment differs from that in Embodiment 2 in that: the pressure in step S32 is maintained at 0.3 Pa; a current of 2 A is passed in step S33, and sputtering coating is performed at a sputtering power of 525 W, and finally an α-phase tantalum superconducting thin film with a thickness of 150 nm is obtained; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0109] The α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and has a characteristic diffraction peak at 38.25°; the surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.646 nm, and the surface morphology has small fluctuations and good uniformity.

[0110] Example 7

[0111] The present embodiment provides a method for preparing an α-phase tantalum superconducting thin film based on a seed layer. The preparation method in the present embodiment differs from that in Embodiment 2 in that: the pressure in step S32 is maintained at 0.3 Pa; in step S33, a current of 2.5 A is passed, and sputtering coating is performed at a sputtering power of 660 W, and finally an α-phase tantalum superconducting thin film with a thickness of 150 nm is obtained; other methods and steps are the same as those in Embodiment 1 and will not be repeated here.

[0112] The α-phase tantalum superconducting film prepared in this embodiment is a (110) crystal phase, and has a characteristic diffraction peak at 38.23°; the surface root mean square roughness of the α-phase tantalum superconducting film prepared in this embodiment is 0.585 nm, and the surface morphology has small fluctuations and good uniformity.

[0113] According to the above embodiments, due to the presence of the niobium metal seed layer, the diffraction angles of the α-phase tantalum superconducting films prepared under different currents in the sputtering coating chambers with different pressures are close, and compared with the ideal diffraction angle of 38.47° of the ideal (110) tantalum, the error is less than 0.25°, and the surface root mean square roughness is small.

[0114] Application Example 1

[0115] This application example provides an application of an α-phase tantalum superconducting film, and the α-phase tantalum superconducting film prepared in Example 2 is used to prepare a high-quality superconducting coplanar waveguide resonant cavity.

[0116] The specific implementation process includes:

[0117] A1. Provide the α-phase tantalum superconducting film prepared in Example 2, spin-coat a photoresist, and then form a coplanar waveguide resonant cavity pattern on the α-phase tantalum superconducting film using exposure and development technology;

[0118] A2. Etching the coplanar waveguide resonant cavity pattern by chemical reaction etching or inductively coupled plasma etching technology to form a coplanar waveguide resonant cavity structure;

[0119] A3. After removing the photoresist, place it in a piranha solution (mixed with 98% concentrated sulfuric acid and 30% hydrogen peroxide solution in a ratio of 3:1) and heat it to 70°C for cleaning for 20 minutes. After cleaning, place it in deionized water for ultrasonic treatment for 2 hours to remove the residual solution on the surface, and then use a nitrogen gun to blow dry, thus preparing a superconducting coplanar waveguide resonant cavity.

[0120] The S21 parameter, i.e., the transmission coefficient, of the superconducting coplanar waveguide resonant cavity is measured using a vector network analyzer. The internal quality factor Q of the superconducting coplanar waveguide resonant cavity is calculated by analyzing the resonant frequency and peak width of the S21 curve. i ; See Figure 6 is the internal quality factor (Q) of the superconducting coplanar waveguide resonant cavity at different frequencies. i ), where n represents the number of photons equivalent to the energy input to the resonant cavity, Q i represents the internal quality factor of the superconducting coplanar waveguide resonant cavity;

[0121] As can be seen from the figure, in the frequency range of 4 to 8 GHz, under single photon energy input (n = 1), the internal quality factor Q i More than 1×10 6 , up to 2×10 6 The high-quality superconducting coplanar waveguide resonant cavity proves that the single (110) crystal phase grown α-phase tantalum superconducting film prepared by the preparation method of the α-phase tantalum superconducting film based on the seed layer in the present invention has extremely low microwave loss and can be applied to various superconducting quantum devices.

[0122] In summary, the present invention uses a DC magnetron sputtering process to sequentially grow a niobium metal seed layer and an α-phase tantalum superconducting film on a substrate. By introducing a niobium metal seed layer, the interlayer lattice mismatch of the α-phase tantalum superconducting film can be reduced, and a single (110) crystal phase-grown α-phase tantalum superconducting film can be prepared at room temperature. The XRD spectrum of the prepared (110) crystal phase α-phase tantalum superconducting film has a characteristic diffraction peak at 38.47°, with an error of ±0.25°; and the present invention can also use a DC magnetron sputtering device with multiple sputtering coating chambers, and use a DC magnetron sputtering process to perform sputtering sequentially at room temperature, which greatly reduces the equipment cost, and the process is highly stable, thereby providing a more reliable material basis for the development of superconducting quantum computing. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0123] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing an α-phase tantalum superconducting thin film based on a seed layer, characterized in that: The preparation method comprises the following steps: S1. providing a substrate; S2, growing a niobium metal seed layer on the upper surface of the substrate by using a DC magnetron sputtering method; S3. Using a DC magnetron sputtering method, grow an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate.

2. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 1, characterized in that: The substrate in step S1 includes one of a sapphire substrate, a silicon substrate, a thermally oxidized silicon substrate, and a magnesium oxide substrate.

3. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 1, characterized in that: The equipment used for the DC magnetron sputtering method in step S2 is a DC magnetron sputtering equipment, and the DC magnetron sputtering equipment includes a niobium sputtering coating chamber, and the target material used in the niobium sputtering coating chamber is a niobium metal target material; The specific steps of growing a niobium metal seed layer on the upper surface of the substrate include: S21, placing the substrate in the niobium sputtering coating chamber, and pumping the vacuum degree to 3×10 -5 Below Pa; S22, introducing working gas into the niobium sputtering coating chamber to maintain the pressure in the niobium sputtering coating chamber at a preset value; S23, applying current to the target material, performing sputtering coating at a certain sputtering power, so that niobium metal is sputtered from the target material to the upper surface of the substrate.

4. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 3, characterized in that: The pressure in step S22 is maintained at 0.3Pa to 1Pa; the current applied in step S23 is 0.5A to 2.5A, the sputtering power is 300W to 1000W, and the sputtering coating rate is 0.5nm / s to 2nm / s.

5. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 1, characterized in that: The thickness of the niobium metal seed layer in step S2 is 5 nm to 50 nm.

6. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 1, characterized in that: The device used for the DC magnetron sputtering method in step S3 is a DC magnetron sputtering device, the DC magnetron sputtering device includes a tantalum sputtering coating chamber, and the target material used in the tantalum sputtering coating chamber is a tantalum metal target material; The specific steps of growing an α-phase tantalum superconducting thin film on a side of the niobium metal seed layer away from the substrate include: S31, transferring the sample with the niobium metal seed layer grown thereon to the tantalum sputtering coating chamber, and pumping the vacuum degree thereof to 3×10 -5 Below Pa; S32, introducing working gas into the tantalum sputtering coating chamber to maintain the pressure in the tantalum sputtering coating chamber at a preset value; S33, applying current to the target material, and performing sputtering coating at a certain sputtering power, so that the tantalum metal is sputtered from the target material to the side of the niobium metal seed layer away from the substrate.

7. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 6, characterized in that: The pressure in step S32 is maintained at 0.3Pa to 1Pa; the current applied in step S33 is 0.5A to 2.5A, the sputtering power is 300W to 1000W, and the sputtering coating rate is 0.5nm / s to 2nm / s.

8. The method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to claim 1, characterized in that: The thickness of the α-phase tantalum superconducting film in step S3 is 100 nm to 300 nm.

9. An α-phase tantalum superconducting thin film prepared by the method for preparing an α-phase tantalum superconducting thin film based on a seed layer according to any one of claims 1 to 8.

10. An application of an α-phase tantalum superconducting film, characterized in that: The application of the α-phase tantalum superconducting film in superconducting quantum devices, wherein the α-phase tantalum superconducting film is prepared by the preparation method of the α-phase tantalum superconducting film based on the seed layer according to any one of claims 1 to 8.

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